The wheel covers for use with vehicle wheels have become various in their design these days and those which are made not of metals but synthetic resins have become popular from the viewpoint of reducing the weight of vehicle. On the other hand, the speed of vehicles has become higher and higher, following the development of highways. The falling-off of the wheel covers from the vehicle wheels will therefore cause serious accident and it is thus seriously needed that the wheel covers are so reliably attached to the vehicle wheels that they can be prevented from falling off the vehicle wheels.
Some of the conventional manners of mounting the wheel cover on the wheel rim comprise fixing a spring wire or plate to the holder wall (or flange portion) on the back circumference of the wheel cover and engaging this spring member such as the spring wire or plate with the hump portion of the wheel rim. However, these manners of engaging the spring member directly with the wheel rim have the following drawbacks.
The spring member is contacted with the wheel rim at a few portions thereof. Therefore, its rigidity must be made strong and its attaching to the wheel rim must be made solid. Strong urging force is thus applied locally to those portions of the wheel rim with which the wheel cover is attached, and this causes a creaking sound while the vehicle is running.
When the rigidity of the spring member is made strong, the flexibility thereof becomes worse. As the holder wall of the wheel cover by which the spring member is held becomes fatigued and deformed, the force with which the wheel cover is fixed to the wheel rim is extremely reduced. When a new wheel cover is to be attached, therefore, extremely large force is needed to detach the old wheel cover from the wheel rim and attach the new one to it, but when the wheel covers are repeatedly exchanged like this and used, they become prone to easily fall off from the wheel rims by extremely small force applied from outside while the vehicle is running.
The manner of urging metal parts such as the spring member directly onto the wall of the wheel rim damages and rusts the wheel rim wall. When the rust on the wheel rim wall progresses, the progressed rust will make the running vehicle seriously unsafe.
The wheel cover disclosed by U.S. Pat. No. 4,027,919 comprises inserting loop projections, which extend outwardly from a metal ring element, into passageways in the flange portion and pressing the loop projections onto the wheel rim to hold the wheel cover fixed to the wheel rim. However, the force with which the wheel cover is fixed to the wheel rim is insufficient in this case and it will happen that the wheel cover falls off from the wheel rim or will idle on the wheel rim while the vehicle is running. In addition, the wheel rim will be damaged by this manner of pressing the loop projections onto the wheel rim, as described above.
In order to prevent the wheel rims from being damaged, DEP No. 2937083.0 (Pre-opened Japanese Application No. Sho 56-47301) discloses that the projections are covered by cover pieces formed integral to the wheel cover and then pressed onto the wheel rim. However, engagement between brackets (which correspond to the above-mentioned projections) of a wire ring and the wheel cover is complicated in this case. In addition, this wheel cover cannot be applied to all of wheel rims which are various in size, and it is not economical accordingly.
Pre-opened Japanese Utility Model Application No. Sho 56-25601 discloses that those portions of the wheel cover which are pressed onto the wheel rim are formed as engagement pieces made of synthetic resin and that these engagement pieces are pressed onto the wheel rim by a wire ring attached to the wheel cover. However, the arrangement of pressing the synthetic resin pieces onto the wheel rim is insufficient in construction and the sufficiency of the engagement force between the wheel cover and the wheel rim is doubtful. Japanese Utility Model Publication No. Sho 60-7921 discloses that engagement pieces which are slidably guided by passageways in struts of the wheel cover are pressed onto the wheel rim, but it may be said that this concept is derived from the abovementioned U.S. Pat. No. 4,027,919.